Hello - I'm new to carbon transfer printing. I've made eight single transfer carbon prints so far this week, but already I want to try double transfer. I wanted to continue to use fixed out photo paper, but Nadeau's book indicates that I can't do that. He states that I need to coat a paper with a relatively soft gelatin for double transfer. He states that a single transfer paper cannot be used as soon as dry, because quite a bit of time is need for the chrome alum to harden the gelatin. However, he does not indicate how long I need to wait after drying before I can use the double transfer paper. Does anyone know? He states that potassium alum be used, not chrome alum, because the gelatin needs to be softer. So I take it I wouldn't need to wait as long? Also, what is recommended double transfer paper if one prefers a very smooth surface, about the weight of Ilford MGIV fiber paper I've been using for single transfer? Thanks in advance for any and all assistance!